1. Field of the Invention
The invention relates to a rotary printing machine with a plate cylinder, a transfer cylinder and an impression cylinder, wherein the transfer cylinder has a rubber blanket arranged on a support. Rotary printing machines of this type operate in accordance with an indirect printing process such as an offset printing process or an indirect gravure printing process.
2. Description of the Related Art
During operation of a rotary printing machine with a plate cylinder, a transfer cylinder and an impression cylinder, the plate cylinder presses onto the transfer cylinder and the transfer cylinder is pressed against the impression cylinder with a web running between the transfer cylinder and the impression cylinder. The rubber blanket on the transfer cylinder is compressed by the plate cylinder and the impression cylinder producing a flexure work of the rubber blanket. As a result of the flexure work, dissipation energy is produced in the rubber blanket of the transfer cylinder during rolling contact with a plate cylinder and the impression cylinder. The dissipation energy produces an undesired heating of the rubber blanket. One solution for removing the undesired heating is to incorporate and an internal cooling system for the transfer cylinder as disclosed, for example, in accordance with European Patent No. EP 0 697 284 A1. However, both the production and the operation of this type of internal cooling is complicated thereby adding significantly to manufacturing and operating costs.
Another solution described in German reference DE 196 19 655 A1 improves the heat transfer between the rubber blanket and the transfer cylinder on which the rubber blanket is mounted to comply with prescribed temperatures of a rubber blanket. It is proposed that the rubber blanket contain a heat-dissipating inlay or underlay, which leads the heat away better radially toward the transfer cylinder. A problem with this solution is that local heating differences in the rubber blanket heat the transfer cylinder to a correspondingly different extent. The local temperature differences of this kind in the rubber blanket may be caused by the subject matter being printed or may be established as a result of different compressibility of the rubber blanket, for example as a result of inhomogeneities in the rubber blanket. The nonuniform heating of the transfer cylinder may in turn lead to deformations such as, for example, a curvature of the longitudinal axis of the transfer cylinder which disrupt the ink transfer and impair the printing quality.
The object of the present invention is to provide a rotary printing machine with a transfer cylinder that minimizes the temperature variation around the circumference so that the temperature is as uniform as possible over the circumference of the transfer cylinder.
The object of the present invention is achieved by a rotary printing machine, comprising a plate cylinder, a transfer cylinder and an impression cylinder. The transfer cylinder is arranged between the plate cylinder and the impression cylinder for transferring an image to a web passing between the transfer cylinder and the impression cylinder. The transfer cylinder comprises a rubber blanket arranged on a support with a highly thermally conductive layer arranged between the rubber blanket and the support for distributing localized heat from the rubber blanket along a surface of the transfer cylinder. The highly conductive layer comprises a material having a thermal conductivity (a) substantially higher than the thermal conductivity of steel.
The highly thermally conductive layer arranged beneath the rubber blanket distributes heat differences in the direction of the surface of the transfer cylinder (i.e., in the longitudinal and circumferential directions), and thus contributes to making the temperature of the transfer cylinder more uniform in these directions. Inevitably, the highly thermally conductive layer will also conduct heat to the transfer cylinder, but this is typically an insignificant portion. If necessary, the radial heat conduction toward the transfer cylinder may optionally be counteracted by providing a thermally insulating layer. Accordingly, the thermally conductive layer of the present invention counteracts nonuniform heating of the transfer cylinder and the bulging of the transfer cylinder associated with nonuniform heating, thereby providing the proper preconditions for a good printing quality (good impression). In addition, the thermally conductive layer on the rubber-blanket support may be produced cost-effectively.